Automatic ice cube machines are widely used in restaurants, bars, hotels, etc. Such commercial machines typically form ice cubes by freezing a flowing stream of water on the chilled evaporator portion of a refrigeration system. After the ice has been formed to the desired thickness, the evaporator is heated, thereby melting the bond between the ice and the evaporator and allowing the ice to then fall or be pushed into an ice holding bin below. Heating of the evaporator is typically accomplished using "hot gas defrost," whereby hot refrigerant gas from the compressor is caused to bypass the condenser and go directly into the evaporator. The hot gas defrost cycle ends after the ice cubes have fallen away from the evaporator.
Such a hot gas defrost cycle adversely affects the capacity and energy efficiency of the ice machine. The ice making capacity is significantly reduced because: 1) the machine spends a substantial portion of its time defrosting, during which time no useful refrigeration is provided, 2) the ice machine melts some ice during defrost, and 3) the heat added to the evaporator during hot gas defrost must be removed from the evaporator before freezing can resume--which means that the machine's refrigerating capacity is being used to remove heat added during defrost rather than to make ice. Also, because the ice making machine is consuming energy during the defrost process but is not making ice, the energy efficiency is significantly lower than that of an ice machine with no hot gas defrost cycle.
The capacity and energy efficiency of an ice making machine are also affected by the refrigeration system's condensing temperature. It is well known that raising condensing temperature in a refrigeration system leads to a reduction of the heat transfer output and efficiency of the system. Cube making ice machines often are designed to have a higher condensing temperature than would otherwise be required in order to assure that sufficiently hot refrigerant gas is available to provide a quick defrost. This leads to lower capacity and efficiency.
Another disadvantage of ice machines using hot gas defrost is their reduced service life. An ice machine which utilizes a hot gas defrost cycle constantly cycles between warm and cold. This constant thermal cycling and the corresponding refrigerant pressure variations causes the main components to wear out faster than they would otherwise.
Various machines and methods for making ice have been available heretofore. For example, U.S. Pat. Nos. 2,610,476 and 2,990,199 to C. Field, 2,613,511 to E. C. Walsh, 2,683,356 and 2,683,359 to Charles M. Green, Jr., and 2,803,950 to J. R. Bayston all describe methods for making ice on a flexible or deformable surface which do not require a hot gas defrost cycle. However, all of these methods produce randomly shaped pieces of ice as each method fractures the ice as it is broken free of the deformable freezing surface. None of these methods allow the ice to have a controlled and consistent cross-sectional shape.
U.S. Pat. No. 4,412,429 to Vance L. Kohl describes an ice making method providing a jacket around an evaporator tube having intersecting ridges which define an array of sites for growing the ice cubes, with the "bottom" of each site being in close contact with an area of evaporator tube for freezing water applied thereto. During harvesting, water is circulated through the jacket to uniformly melt and loosen the cubes so they may fall away. The jacket may be made of a flexible plastic material so that filling said jacket with water during said harvest mode causes flexing thereof to help dislodge the ice cubes or particles.
While this method does not use a hot gas defrost and does use some flexing to remove ice from the freezing surface, it harvests the ice primarily through melting. The "bottom" of each freezing site (the primary contact area between ice and evaporator) is securely fastened to the evaporator tube and is not flexible; the ice can only be freed from this area by melting. Only the periphery of each freezing site is capable of any flexing.
Commercially available flaker-type ice machines do not utilize a hot gas defrost cycle, but they cannot make hard, clear, consistently-shaped ice cubes.
An objective of this invention is to provide a machine or apparatus for making hard, substantially clear, uniformly shaped ice cubes, which does not require hot gas defrost and which thus provides greater ice producing capacity, greater energy efficiency and longer service life than conventional cube making ice machines.